AN AUTOMATED CO2 CONTROL-SYSTEM FOR PLANT-GROWTH CHAMBERS AND ITS USE TO ESTIMATE NET PLANT CO2 EXCHANGES

Control of CO2 concentration within growth chambers is necessary to compensate photosynthetic CO2 depletion or to study the effects of elevated CO2 concentrations on plant physiology. A microcomputer-driven CO2 control system was developed to maintain independently, in four growth chambers, a CO2 concentration between 50 and 10 000 μmol mol-1. Air samples were taken sequentially every 12 min in each chamber and their CO2 concentrations measured by an infrared gas analyser. These measurements allow for the calculation of photosynthetic rate. Pure CO2 was delivered at the rate of its assimilation by plants by injecting a small, constant quantity at a frequency modulated by the previously calculated photosynthetic rates. The continually updated daily patterns of photosynthesis could be displayed on the computer screen. Examples of daily patterns of CO2 regulation and photosynthetic rates are given together with photosynthetic response of water hyacinth (Eichhornia crassipes) canopies to elevated CO2 levels. The latter example advocates the use of growth chambers equipped with process control systems for direct experiment rather than only for plant conditioning. © 1992 Silsoe Research Institute.